A side part of an automobile includes frames such as pillars extending in the height direction of the automobile and rails extending in the forward-rearward or lateral direction of the automobile. These pillars and rails each typically include an inner panel and an outer panel facing the inner panel to form a closed space between the outer panel and the inner panel. The entire pillar or rail thus has a hollow structure.
The pillar and the rail include, within an inner space (closed space), metal members for reinforcing the pillar and the rail. Patent Document 1 (JP 2007-326376 A), for example, discloses a pillar structure including metal reinforcements within a closed space.
FIG. 9 illustrates a pillar structure disclosed in Patent Document 1. As illustrated in FIG. 9, this pillar structure includes an outer panel 12 and an inner panel 14 that together form a closed section. This closed section includes an outer reinforcement (hereinafter abbreviated as an “outer R/F”; this abbreviation similarly applies to other members) 16 along the outer panel 12 and an inner R/F 18 along the inner panel 14. This pillar structure further includes an auxiliary R/F 40 along the outer R/F 16. The auxiliary R/F 40 is typically made of a metal, similar to the outer R/F 16 and the inner R/F 18.